Alan E. Wakeling

ICI 182,780 (Faslodex™) Development of a Novel, "Pure" Antiestrogen

The nonsteroidal antiestrogen tamoxifen is well established as an effective treatment for patients with breast carcinoma, both for the treatment of metastatic disease and as an adjuvant to surgery for patients with primary breast carcinoma. In addition to exerting antagonistic effects on the estrogen receptor, tamoxifen and its derivatives act as partial agonists on certain tissues. These agonistic effects, for example, endometrial stimulation and stimulation of tumor growth after previous response to tamoxifen, may limit their clinical efficacy. ICI 182,780 (Faslodex™) from AstraZeneca (Cheshire, United Kingdom) is a novel, steroidal estrogen antagonist that was designed to be devoid of estrogen agonist activity in preclinical models.

Mechanisms of Tumor Regression and Resistance to Estrogen Deprivation and Fulvestrant in a Model of Estrogen Receptor–Positive, HER-2/neu-Positive Breast Cancer

HER-2/neu in breast cancer is associated with tamoxifen resistance, but little data exist on its interaction with estrogen deprivation or fulvestrant. Here, we used an in vivo xenograft model of estrogen receptor (ER)-positive breast cancer with HER-2/neu overexpression (MCF7/HER-2/neu-18) to investigate mechanisms of growth inhibition and treatment resistance. MCF7/HER-2/neu-18 tumors were growth inhibited by estrogen deprivation and with fulvestrant, but resistance developed in 2 to 3 months. Inhibited tumors had reductions in ER, insulin-like growth factor-I receptor (IGF-IR), phosphorylated HER-2/neu (p-HER-2/neu), and phosphorylated p42/44 mitogen-activated protein kinase (p-MAPK). p27 was increased especially in tumors sensitive to estrogen deprivation. Tumors with acquired resistance to these therapies had complete loss of ER, increased p-HER-2/neu, increased p-MAPK, and reduced p27. In contrast, IGF-IR and phosphorylated AKT (p-AKT) levels were markedly reduced in these resistant tumors. The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor gefitinib, which can block EGFR/HER-2/neu signaling, significantly delayed the emergence of resistance to both estrogen deprivation and fulvestrant. Levels of p-MAPK and p-AKT decreased with gefitinib, whereas high ER levels were restored. Eventually, however, tumors progressed in mice treated with gefitinib combined with estrogen deprivation or fulvestrant accompanied again by loss of ER and IGF-IR, increased p-HER-2/neu, high p-MAPK, and now increased p-AKT. Thus, estrogen deprivation and fulvestrant can effectively inhibit HER-2/neu-overexpressing tumors but resistance develops quickly. EGFR/HER-2/neu inhibitors can delay resistance, but reactivation of HER-2/neu and signaling through AKT leads to tumor regrowth. Combining endocrine therapy with EGFR/HER-2/neu inhibitors should be tested in clinical breast cancer, but a more complete blockade of EGFR/HER-2/neu may be optimal.

The future of new pure antiestrogens in clinical breast cancer

SummaryThe rationale for seeking to identify new pure antiestrogens was based on the recognition that existing antiestrogens, exemplified by tamoxifen, all possess partial agonist (estrogenic) activity. Conceptually, pure antiestrogens should be more effective than tamoxifen in ablating the mitogenic action of estrogens on breast tumor growth. The discovery and properties of the pure antiestrogens ICI 164,384 and ICI 182,780 are described and contrasted with those of tamoxifen. Key characteristics of these compounds which may be of particular relevance to their therapeutic application in the treatment of breast cancer are described. These include experimental data which predict efficacy in patients whose disease recurs during tamoxifen treatment, and the potential for pure antiestrogens to demonstrate greater efficacy than tamoxifen in first-line treatment of advanced breast cancer. The data imply that gains in efficacy could emerge as more rapid, more complete, or longer-lasting tumor remissions. Clinical trials with ICI 182,780 will reveal whether one or more of these predictions is correct.

The importance of tamoxifen metabolism in tamoxifen-stimulated breast tumor growth

The acquired ability of tamoxifen to stimulate tumor growth has been suggested as one mechanism for the development of treatment failure in breast cancer. We have reported that tamoxifen-stimulated MCF-7 breast tumors in nude mice display reduced tamoxifen levels as compared with tamoxifen-inhibited tumors and an altered metabolite profile with isomerization oftrans-4-hydroxytamoxifen to a weak antiestrogen and the production of metabolite E, an estrogenic metabolite. To investigate further the importance of tamoxifen metabolism in this model, we quantified levels of tamoxifen and major metabolites in tamoxifen-stimulated as compared with tamoxifen-inhibited MCF-7 tumors growing in nude mice and employed tamoxifen analogs resistant to metabolism. Tamoxifen-stimulated tumors have a relative abundance ofcis-4-hydroxytamoxifen and metabolite E. However, in vivo treatment of mice carrying tamoxifen-stimulated tumors with fixed-ring nonisomerizable tamoxifen analogs or with nafoxidine, a nonsteroidal antiestrogen with a different structure, nonetheless resulted in tumor growth stimulation. Tumors were also stimulated by a deoxytamoxifen analog resistant to conversion to metabolite E. Growth of tamoxifen-stimulated tumors was inhibited by a pure steroidal antiestrogen, ICI 182, 780, suggesting the need for clinical trials of this drug in patients with tamoxifen resistance. Growth of tamoxifen-stimulated tumors was further stimulated by estrogen replenishment, and this estrogen stimulation could be blocked by tamoxifen indicating that tamoxifen has both agonist and antagonist properties in these tumors. This study suggests that tamoxifen-stimulated tumor growth in this model is not due to isomerization or metabolism of tamoxifen to less antiestrogenic or more estrogenic metabolities. The mechanisms by which tamoxifen acquires more potent in vivo agonist properties, resulting in tumor growth stimulation over time, remain to be defined.

Growth factors and their receptors: New targets for prostate cancer therapy

Stimulation of the signal transduction pathway of the epidermal growth-factor receptor (EGFR) tyrosine kinase family of receptors in tumor cells enhances cellular proliferation, prevents apoptosis, and promotes tumor-cell mobility, adhesion, and invasion. Therapeutic approaches used to target the EGFR and its signal transduction cascade include (1) monoclonal antibodies (eg, cetuximab [IMC-C225]) directed against the extracellular binding domain of the receptor; and (2) trastuzumab, a monoclonal antibody binding to the HER2 receptor; immunotoxin conjugates use an antibody directed against EGFR joined to a cell toxin. All are in clinical trials for a number of cancers, including prostate cancer. Antisense strategies are in preclinical development. Low-molecular-weight inhibitors of the EGFR tyrosine kinase also in clinical development include OSI-774, PD182905, PKI-166, CI-1033, and ZD1839. ZD1839 has shown encouraging results in patients with prostate cancer in phase 1 trials. mn

Epidermal growth factor receptor tyrosine kinase inhibitors.

Clinical trials of selective small-molecule inhibitors of epidermal growth factor receptor tyrosine kinase activity have shown that these targeted inhibitors of proliferative signal transduction provide well-tolerated antitumour activity in patients. Preclinical pharmacology studies illustrate the potential use of these new cancer therapeutics in combination with chemotherapy, radiotherapy and hormone therapy, and in chemoprevention, in a spectrum of solid human tumours.

Modulation of Epidermal Growth Factor Receptor in Endocrine‐Resistant, Estrogen‐Receptor‐Positive Breast Cancer

Abstract: An increasing body of evidence demonstrates that growth factor networks are highly interactive with estrogen receptor signaling in the control of breast cancer growth. As such, tumor responses to antihormones are likely to be a composite of the estrogen receptor and growth factor inhibitory activity of these agents. The modulation of growth factor networks during endocrine response is examined, and in vitro and clinical evidence is presented that epidermal growth factor receptor signaling, maintained in either an estrogen receptor‐dependent or a receptor‐independent manner, is critical to antihormone‐resistant breast cancer cell growth. The considerable potential of the epidermal growth factor receptor‐selective tyrosine kinase inhibitor Iressa (ZD 1839) to efficiently treat, and perhaps even prevent, endocrine‐resistant breast cancer is highlighted.

The biology and physiology of ‘Nolvadex’ (tamoxifen) in the treatment of breast cancer

SummaryAfter more than a quarter of a million patient years experience with tamoxifen in the clinic, it is perhaps appropriate to re-examine the working hypothesis for the activity of this drug. This hypothesis states that tamoxifen is an anti-oestrogen which exerts its anti-tumour activity by competing for and binding to cytoplasmic oestrogen receptor protein in the tumour.The evidence that tamoxifen is an anti-oestrogen in animals and man is seen to vary from species to species and between target organs within a species. The balance of the evidence supports the conclusion that this drug acts as an oestrogen antagonist in man.If the activity of this drug were confined to an effect mediated by the oestrogen receptor (ER), there should be a clear correlation between the anti-tumour effect of tamoxifen and the presence of ER. The clinical and pre-clinical data are reviewed. Whilst the majority of the evidence points to an effect in advanced breast cancer mediated through the ER, there are data that show the correlation is not absolute. The data are examined and the evidence for non-receptor mediated anti-tumour activity is reviewed.We conclude that whilst the majority of the activity of tamoxifen is that of an anti-oestrogen mediated through the ER, compelling evidence exists that this may not be its only anti-tumour activity at normal clinical doses. These findings might explain tamoxifens activity in some ER negative tumours.

NEW EGF-R SELECTIVE TYROSINE KINASE INHIBITOR REVEALS VARIABLE GROWTH RESPONSES IN PROSTATE CARCINOMA CELL LINES PC-3 AND DU-145

The effect of an EGF‐R selective tyrosine kinase inhibitor ZM252868 was evaluated on the proliferation of PC‐3 and DU‐145 prostate cancer cell lines, which are purported to utilize an EGF‐R‐mediated autocrine pathway for regulation of cell growth. Basal growth of DU‐145 cells was inhibited in a dose‐dependent manner by the inhibitor, showing a 70% reduction at 1 μM, whilst the growth of PC‐3 cells was not affected at this concentration. In the presence of 0.1 μM inhibitor, EGF and TGFα‐stimulated DU‐145 cell growth was decreased to below basal levels, while only TGFα‐stimulated PC‐3 cell growth was inhibited at a 1‐μM concentration. Any growth responses to aFGF, bFGF, KGF, IGF1 and PDGF by DU‐145 and PC‐3 cells were unaffected by the inhibitor at concentrations of 1 μM or less. Additionally, the distribution of immunoreactive EGF‐R varied between DU‐145 and PC‐3 cells, with EGF‐R being predominately located on the cell membrane and in the cytoplasm, respectively. Int. J. Cancer 71:1010‐1018, 1997.

Effects of short-term antiestrogen treatment of primary breast cancer on estrogen receptor mRNA and protein expression and on estrogen-regulated genes

SummaryEffects of the pure antiestrogen ICI182780 and tamoxifen on ER-protein, ER-mRNA, and estrogen-regulated mRNA expression were analysed using matched pretreatment core-cut biopsies and post-treatment mastectomy samples from 43 ER positive human breast cancers. Sixteen controls received either no preoperative treatment (n = 9) (7 days) or placebo (n = 7) (median 21 days) prior to primary surgery. Nineteen patients received ICI182780 6 mg/day (n = 10) or 18 mg/day (n = 9) for 7 days. Eight patients were given preoperative tamoxifen (4 × 40 mg-day 1, 20 mg/day thereafter, median 21 days). ER-protein expression was assessed on pre and post treatment samples by immunocytochemistry. ER, pS2, pLIV1, and actin-mRNA expression was determined by northern analysis on post-treatment samples only. ER-mRNA levels were similar to controls following ICI182780 or tamoxifen treatment. However ER-protein levels were significantly suppressed by ICI182780, particularly at the higher dosage (p = 0.0013). Tamoxifen had no significant effect on ER-protein levels. The ER-mRNA and ER-protein contents of control tumors were linearly related (Spearman r = 0.719, p = 0.006). A similar relationship between pretreatment protein and post ICI182780 treatment mRNA levels was observed (r = 0.652, p = 0.005). However, comparison of post ICI182780 treatment protein and mRNA results shows a loss of linearity through a reduction in protein without concurrent loss of mRNA (r = 0.28, p = 0.257). pS2 mRNA hybridization was lower in ICI182780 treated samples than controls (Mann-Whitney p = 0.035) but was unaffected by tamoxifen. pLIV1 mRNA hybridization was uninfluenced by either treatment. Short term exposure of breast tumors to ICI182780 appears to produce a greater inhibition of estrogen-induced transcriptional events than tamoxifen. These effects appear to occur without a concurrent reduction in ER mRNA levels.